Conventionally, in an optical type granule sorting machine, before sorting operation, an operator changes a reference threshold set in advance in optical detection means to adjust a sensitivity level. The adjustment of the sensitivity level allows adjustment of the type of foreign substances (glass pieces, stones, and the like) to be sorted and removed from sorting targets or adjustment of the type of colored granules (nonconforming granules, milky rice, slightly altered rice, and the like) to be sorted and removed from sorting targets. Setting the sensitivity level at a proper value as described above allows precise removal of foreign substances, colored granules, and other nonconforming granules. That is, too low sensitivity causes imprecise determination of whether sorting granules are conforming or nonconforming granules and therefore causes unintended operation of exclusion means, resulting in nonconforming granules being mixed in with conforming granules. On the other hand, too high sensitivity causes excessive exclusion operation of the exclusion means and hence causes conforming granules to be sorted as well as nonconforming granules, resulting in a decrease in yield.
The adjustment of the sensitivity level before the sorting operation is cumbersome for an operator, or frequent adjustment of the sensitivity level could cause instability in sorting accuracy. To solve the problem described above, there has been proposed a color sorting machine that displays an image of a granule captured with a CCD sensor or any other image pickup means and allows an operator who looks at the displayed image to perform the sensitivity adjustment (see Patent Literature 1).
The color sorting machine includes transfer means for continuously transferring granules and illumination means for illuminating the granules being transferred in a detection position. The color sorting machine further includes image pickup means for picking up an image of the illuminated granules in the detection position and exterior shape processing means for outputting the contour shape of a granule in the form of exterior shape binary data based on comparison between an image signal from the image pickup means and an exterior shape threshold. The color sorting machine still further includes no-conformation determination means for determining a granule having a portion having a density greater than a threshold corresponding to a predetermined density to be a nonconforming granule and outputting the nonconforming portion of the nonconforming granule in the form of nonconforming pixel binary data. The color sorting machine still further includes granule display means for combining the exterior shape binary data from the exterior shape processing means with the nonconforming pixel binary data from the no-conformation determination means and displaying the combined data and nonconforming granule display means for displaying the nonconforming pixel binary data from the no-conformation determination means. The color sorting machine still further includes a display adjustment mechanism including threshold adjustment means for allowing an operator who looks at the display means to change the threshold.
The thus configured color sorting machine, which allows the operator to adjust the sensitivity after checking a nonconforming granule having been determined to be nonconforming based on set sensitivity by using the display means, is advantageously effective in that the sensitivity can be adjusted more accurately.
The color sorting machine described in Patent Literature 1 displays an image of a granule on the operation panel and allows the operator who looks at the displayed image to adjust the sensitivity. In this process, the operator could be undesirably required, for example, to make decision on or possess knowhow about, for example, the type and degree of foreign substances to be sorted and removed or the type and degree of colored granules to be sorted and removed.